The present invention concerns a method for the optimization of the payload of a telecommunication satellite with several spots, known as a multispot or multibeam satellite. This type of satellite allows several antenna spots to be used on board the satellite to cover contiguous geographical zones, instead of a single broad spot.
Such multispot satellites allow several radiofrequency links to be established occupying the same frequency band on different spots. An example of multispot configuration is illustrated in FIG. 1. Signals are sent towards a satellite 3 on an uplink LM by a terrestrial station 2 such as a gateway connected to an internet backbone 5. These signals are then processed at the level of the satellite 3 then retransmitted on a downlink LD in the form of a plurality of spots or spots SP1 to SP8.
In addition, certain multispot satellites allow polarized transmissions to be emitted (and received): the polarization can be linear (in this case the two directions of polarization are respectively horizontal and vertical) or circular (in this case the two directions of polarization are respectively circular left or circular right).
It will be noted that in the example of FIG. 1, the uplink leaving the station 2 uses two polarizations with four channels for each polarization, respectively Ch1 to Ch4 for the first polarization and Ch5 to Ch8 for the second polarization. The eight channels Ch1 to Ch8, after processing by the payload of the satellite 3 will form the 8 spots SP1 to SP8 (one channel being associated with one spot in this example).
The payload of the satellite designates the part which allows it to fulfil the mission for which it was designed, i.e. for a telecommunication satellite 3 such as that shown in FIG. 1, to ensure the reception, processing (frequency conversion, filtering, amplification) and re-emission of the telecommunication signals issued from the terrestrial station 2. The payload essentially comprises the antennae of the satellite and the transponders (and not the equipment for control, propulsion or electrical power equipment which belong to the platform of the satellite).
FIG. 2a shows in a known manner a functional block diagram of an architecture of payload 10 with multispot emission on the downlink. After reception and selection of the polarization, the signal received from a gateway is amplified by a LNA low noise amplifier 12. The signal is then separated in Ns uplink channels by a signal divider device 13. The Ns uplink channels are then translated in frequency by a frequency converter circuit 14 generally formed by a local oscillator and are filtered by an input filter 15 (of the pass band filter type) so as to form Ns channels in accordance with the frequency plan of the downlink. The local oscillator is most often constituted by a voltage controlled quartz VCO (Voltage Controlled Oscillator) with a phase lock loop. The Ns translated frequency channels are amplified through a power amplifier 16 HPA (High Power Amplifier) generally formed by a channel amplifier 17 CAMP (Channel AMPlifier) and a travelling wave tube amplifier 18 TWTA forming Ns downlink spot signals. The channel amplifiers 17 are generally gain command amplifiers which allow the power level of the signals to be regulated at input of the travelling wave tubes 18. The tubes 18 can be replaced by solid state power amplifiers SSPA. It is likewise possible to use more sophisticated architectures comprising devices of the MPA type (multiport amplifier) offering the advantage of flexibility. Each of the Ns spot signals is then filtered through an output pass band filter 19, and is then sent on a feed 20 such as a feedhorn towards a reflector for the formation of a spot. According to this configuration, if the number of gateways is designated by NGW, the payload 10 comprises:
2NGW low noise amplifiers 12 LNA;
2NGW signal divider devices 13;
Ns frequency converter circuits 14;
Ns input filters 15;
Ns high power amplifiers 16 HPA;
Ns output pass band filters 19;
Ns feedhorns 20.
However, such a configuration is liable to pose some difficulties. In fact, according to the architecture of FIG. 2a), the number of frequency converters, input filters, channel amplifiers and travelling wave tube amplifiers is equal to the numbers of downlink spots Ns. Consequently, for large-scale systems, the high number of components forming the payload becomes disadvantageous in terms of mass and the launching of the space vehicle. Of course, these disadvantgages likewise have an impact on the associated costs.